Certain diesel engine exhaust after-treatment systems require an addition of reductants, such as hydrocarbons, and/or elevated exhaust temperatures to chemically purge material that has been stored in an exhaust after-treatment device. For instance, a NOx adsorber catalytic converter, often referred to as a NOx trap, operates in two alternative phases: a storage phase and a regeneration phase. During the storage phase, the normal operation of an engine produces a reductant-lean exhaust in which the NOx is oxidized and stored on the NOx adsorber. During the regeneration phase, a reductant-rich exhaust is needed to de-store and convert the NOx into harmless gases. The regeneration phase generally lasts one to fifteen seconds. Similarly, another type of exhaust after-treatment device, being a particulate trap, traps particulates within exhaust flowing through the particulate trap. In order to regenerate the particulate trap, the temperature of the exhaust is raised via a chemical reaction requiring reductant-rich exhaust. The elevated-temperature exhaust with oxygen will be passed through the particulate trap, thereby burning the particulates trapped within the trap.
In order to create the reductant-rich environment and/or the elevated exhaust temperature for the regeneration of the NOx adsorber and particulate trap, additional diesel fuel is introduced into the exhaust. Often, the fuel is injected into the exhaust by an independent fuel injector downstream from the combustion chambers. Although the injection of the fuel creates the reductant-rich exhaust and the elevated exhaust temperatures needed for regeneration, the additional fuel injector increases the cost and complexity of the exhaust after-treatment system.
Moreover, it has been found that typical engine cylinder fuel injectors are incompatible with injecting the additional fuel into the exhaust prior to expelling the exhaust from the combustion chamber. Typical engine cylinder fuel injectors include nozzle outlets that are designed to inject fuel for combustion near top dead center of the engine piston. The injection of additional fuel through the typical engine cylinder fuel injectors after combustion and when the engine piston is closer to bottom dead center causes the fuel to contact the cylinder walls. The fuel can then dilute the lubricating oil, leading to engine malfunctions, such as piston seizure.
The present disclosure is directed at overcoming one or more of the problems set forth above.